Praxis II: Chemistry Exam Prep

Answer: B. Solution is as follows:

DS_rxn° = DS_products° - DS_reactants°

Students must look up the DS° for each product and reactant. The numbers are as follows:

DS° (FeCl_3(s)) = 142.3 J/mol K
DS° (Na_(s)) = 51.3 J/mol K
DS° (Fe_(s)) = 27.2 J/mol K
DS° (NaCl_(s)) = 72.3 J/mol K

Therefore DS_rxn° = [(1mol * 27.2 J/mol K) + (3mol * 72.3 J/mol K) ] - [ (1mol * 142.3 J/mol K) +(3mol * 51.3 J/mol K)]

DS_rxn° = -52.1 J/K

***mole amounts come from the stoichiometry